1. Field of the Invention
The present invention relates to the study and to the optimization of oil reservoir production schemes and models of production behavior of an oil reservoir in order to compare production schemes and to define an optimum scheme considering a given production criterion such as oil recovery, water inflow, production rate, etc.
2. Description of the Prior Art
The study of a reservoir comprises two main stages.
The reservoir characterization stage determines a numerical flow model or flow simulator that is compatible with the real data collected in the field. Engineers have access to only a small part of the reservoir under study (core analysis, logging, well tests) and have to extrapolate these limited data over the entire oilfield to construct the numerical simulation model.
The production prediction stage uses the numerical simulation model to estimate the reserves and production to be obtained in the future or to improve the production scheme in place. This stage is carried out using a numerical simulation model constructed from many data sources, obtained from only a small part of the reservoir. Consequently, an uncertainty notion has to be constantly accounted for in this stage.
In order to properly characterize the impact of each uncertainty on the oil production, the largest possible number of production scenarios has to be tested, which therefore requires a large number of reservoir simulations. Considering the long time required for a flow simulation, it is clearly not conceivable to test all possible scenarios via the numerical flow model. In this context, using the experimental design method can allow construction of a simplified model of the flow simulator as a function of a reduced number of parameters. Experimental designs allow determination of the number and the location in space of the parameters of the simulations to be carried out so as to have a maximum amount of pertinent data at the lowest possible cost. This simple model translates the behavior of a given response (for example the 10-year cumulative oil production) as a function of some parameters. Its construction requires a reduced number of simulations previously defined by experimental designs.
During the production prediction stage, the simplified model is used because it is simple and analytical and, therefore, each simulation obtained by this model is immediate. This saves considerable time. Using this model allows the reservoir engineer to test as many scenarios as are wanted, without having to care about the time required to perform a numerical flow simulation.
The methods disclosed in French patents 2,855,631 and 2,855,633 use simplified models to optimize the production of an oil reservoir or as decision support for managing an oil reservoir, in the presence of uncertainties.
The simplified model obtained using experimental designs implies that the response obtained by the model is a linear function of the parameters taken into account. However, in most cases, this is not true. When the range of evolution of a parameter(s) (permeability, porosity, . . . ) is relatively limited and its contribution is reasonable, its behavior can be assumed to be linear. But when this range of evolution of the parameter(s) becomes too large or when the contribution of the parameter is no longer linear, the linearity hypothesis biases the knowledge of the oil reservoir.
It is therefore necessary to set a criterion allowing detection of non-linearities and to establish an efficient and fast methodology allowing prediction, in an effective manner, of non-linear response behaviors.